1. Field of the Invention
This invention relates in general to an in vivo mechanical energy source. More particularly, it relates to a miniaturized mechanical motor that is small enough to fit inside a percutaneous transluminal device and yet powerful enough to do work.
2. General Description of the Art
Catheters are used in a variety of percutaneous transluminal treatments, such as coronary, cerebral and peripheral angioplasties. The general objective of these treatments is to open obstructions or lesions within a body vessel such as a blood vessel. For example, in percutaneous transluminal coronary angioplasty (PTCA), a guide catheter is introduced at an appropriate location in the patient""s body and routed through the vascular system into the aorta and coronary orifice. A thin and relatively flexible guide wire is advanced through the guide catheter to the arteries, and then steered into side branches (if necessary) to access the obstruction. Once the guide wire has established a path across the obstruction, an xe2x80x9cover-the-wirexe2x80x9d dilatation balloon catheter is passed over the proximal end of the guide wire until the balloon is adjacent the obstruction. The balloon is then inflated by introducing a fluid into the balloon through an inflation lumen in the catheter. The inflated balloon expands against the blockage to dilate the obstructed blood vessel. Another type of balloon catheter known as xe2x80x9cfixed-wire,xe2x80x9d eliminates the need for a separate guide wire by attaching a short flexible guide wire to the distal end of the catheter.
Other methods of treating blocked blood vessels involve the use of miniaturized mechanical devices to cut, abrade, or otherwise open a passage through the obstruction. For example, U.S. Pat. No. 4,936,845 discloses a catheter having a rotating head at its distal end for boring a passageway through an obstructed blood vessel. U.S. Pat. No. 4,854,325 discloses a guide wire that is mechanically driven through a ramming back-and-forth action to assist in forming a pilot passageway through the obstruction. Other miniaturized mechanical devices are disclosed in U.S. Pat. Nos. 5,007,917; 5,011,490; 5,030,201; and 5,059,203.
The mechanical devices disclosed in the above-identified patents are driven by external motors which are connected to the device through a drive shaft extending along the length of the catheter. There are several problems with transmitting mechanical energy down a relatively long drive shaft in a catheter. For example, the drive shaft dissipates a significant amount of the mechanical energy into the patient""s blood vessel. This can cause considerable trauma, and the patient often requires drug treatments to counteract the negative effects. The dissipated mechanical energy also results in large energy losses. Because of the small dimensions of the vascular system, the energy needed at the in vivo work site is typically less than 1 watt. However, due to the tremendous energy losses through the drive shaft, external motors must typically generate about 100 watts in order to produce less than 1 watt at the in vivo work site.
Also, external motors are large and can require complicated connectors for coupling them to the relatively small drive shaft. In addition, drive shafts are relatively rigid, and accordingly, they are difficult to negotiate through the vascular system. Thus, the placement of a drive shaft along the length of a catheter severely compromises the catheter""s flexibility.
U.S. Pat. No. 5,176,141 issued to Bom discloses a disposable ultrasonic catheter that has a rotatable acoustic mirror for directing sound waves outwardly into tissue and for receiving echo sounds and directing the echo sounds to a transducer. The transducer""s output is transmitted to a visual display which displays an ultrasound picture of the tissue whereby one can determine the makeup of the tissue, e.g., hard or soft. A motor is provided in the catheter for rotating the mirror at selected rpm.
The mirror in Bom is a very tiny and light weight acoustic crystal transducer. The motor that rotates the mirror is illustrated only as a cylinder 3 in FIGS. 1-3 of Bom. Bom provides no details about the construction and operation of its motor, except to describe it as a xe2x80x9cmulti-polar microsynchronized motor.xe2x80x9d Bom, col. 4, lines 11-12. Accordingly, the motor disclosed in Bom is not capable of delivering the more than about 0.01 watts of energy that would be needed in order to do any appreciable work such as pumping blood (preferably via a perfusion pump) or operating dottering devices, inflation pumps, atherectomy devices, and other such devices.
Thus, it would be beneficial to provide a mechanical energy source that is powerful enough to do work yet small enough to fit inside a body vessel, thereby allowing the mechanical energy source to be placed inside a percutaneous transluminal device and in close proximity to a load at the distal end of the device.
Thus, it would also be beneficial to provide an in vivo perfusion pump that is specially adapted to be used with an in vivo mechanical energy source, said energy source being powerful enough to do work yet small enough to fit inside a body vessel.
The following terms are used throughout this disclosure and are intended to have the following meanings:
The term xe2x80x9cdistalxe2x80x9d refers to the end of the percutaneous device that is inserted in the patient""s vascular system.
The term xe2x80x9cproximalxe2x80x9d refers to the end of the percutaneous device that is outside the patient""s vascular system.
It is an object of the present invention to provide a method and structure for generating mechanical energy inside the vascular system.
It is also an object of the present invention to provide a method and structure for generating mechanical energy at the distal end of a percutaneous transluminal device.
It is another object of the present invention to provide mechanical energy in close proximity to a miniaturized medical device located at the distal end of a percutaneous transluminal device.
It is yet another object of the present invention to provide a miniaturized mechanical energy source that is powerful enough to do work.
It is yet another object of the present invention to provide an in vivo perfusion pump capable of being used with a miniaturized mechanical energy source that is powerful enough to adequately perfuse a coronary artery.
These and other objects are realized in accordance with the present invention by providing a miniaturized mechanical energy source that is small enough to fit inside a body vessel. The disclosed embodiments of the invention are substantially cylindrical miniaturized motors (xe2x80x9cmicromotorsxe2x80x9d) that measure less than 250 mils in length and less than 80 mils in diameter. In one embodiment, the motor includes a small cylindrical magnet linearly aligned between two sets of driving coils. Current is applied to the driving coils so that they periodically and alternately repel and attract the magnet, thereby driving it back and forth between the two sets of coils. In an alternative embodiment, a sensor is linearly aligned with the magnet and the driving coils. The sensor detects the relative position of the magnet and then directs an external driving circuit to deliver current to the driving coils based on the magnet""s position. The driving coils are connected in series so that the same current flows through both sets of coils.
The disclosed embodiments of the present invention provide several advantages. The sensor delivers current to the driving coils based on the actual position of the magnet, and thus a load placed on the magnet cannot force it out of phase with the driving current. The series connection from one set of driving coils to the other, along with the directions (sense) of the driving coil windings, insures that one set of coils is always repelling the magnet when the other set of coils is attracting it. Additionally, the motor""s linear configuration provides optimal coupling between the driving coils and the magnet. This linear configuration also allows the motor to fit conveniently inside a conventional elongated catheter. These and other features allow the present invention to perform work using motors that are small enough to fit inside a conventional transluminal catheter. The disclosed motors are placed in close proximity to their load, and thus they are not burdened by the considerable power losses associated with transmitting mechanical energy down a relatively long drive shaft.
The present invention may thus be utilized to provide efficient, in vivo mechanical energy to a wide range of loads and applications such as perfusion pumps, dottering devices, inflation pumps, atherectomy devices, delivering vibrational energy to relax arterial muscles, and others.
A particularly advantageous application of the micromotors is disclosed in connection with several embodiments of a novel perfusion pump, which may be used with the disclosed in vivo mechanical energy source.
In one embodiment, the perfusion pump includes an external energy source, a push wire having its proximal end connected to the external energy source, a reciprocating piston connected to the distal end of the push wire, an intermediate tubular chamber surrounding the piston, an intake aperture formed in the chamber wall, and a distal exit tube coupled to the chamber. The external energy source reciprocates the push wire, which reciprocates the piston within the intermediate tubular chamber. The piston draws fluid into the intermediate chamber on its backstroke, thereby filling the chamber with fluid when the piston crosses the intake aperture. Fluid is forced out of the exit hole when the piston moves on its forward stroke.
In another embodiment, the perfusion pump includes a tubular chamber, a piston magnet within the chamber, piston winding coils around the tubular chamber, a valve magnet within the chamber, valve winding coils around the tubular chamber, an intake aperture formed in the chamber wall, and a distal exit tube coupled to the chamber. Electrical energy is provided to the piston winding coils to reciprocate the piston within the tubular chamber, thus providing an in vivo mechanical energy Source. Electrical energy is also provided to the valve windings to periodically move the valve magnet so that it either covers or uncovers the intake aperture. The electrical energy is provided to the piston windings and the valve windings approximately 180 degrees out of phase, so that the valve magnet uncovers the intake aperture whenever the piston moves proximally, and the valve covers the intake aperture whenever the piston moves distally. Accordingly, when the piston moves proximally, it draws fluid through the intake aperture, and when the piston moves distally, it expels fluid through the distal exit tube coupled to the chamber.
In yet another embodiment, the perfusion pump is a double acting pump in which fluid is pumped on both the forward and the back stroke of the piston. The pump includes a tubular chamber, a piston magnet within the chamber, piston winding coils around the tubular chamber, a first valve magnet within the chamber, first valve winding coils around the tubular chamber, a first intake aperture formed in the chamber wall near the first valve magnet, a second valve magnet within the chamber, second valve winding coils around the tubular chamber, a second intake aperture formed in the chamber wall near the second valve magnet, and a distal exit tube coupled to the chamber. Electrical energy is provided to the piston winding coils to reciprocate the piston within the tubular chamber, thus providing an in vivo mechanical energy source. Electrical energy is also provided to the first and second valve windings to periodically move the valve magnet so that it either covers or uncovers the intake aperture. The electrical energy is provided to the piston windings and the valve windings such that the valve magnets alternately cover and uncover the intake apertures.
In the double acting embodiment, two of the magnets are in phase with each other but 180xc2x0 out of phase with the third magnet (i.e., two magnets move forward while the third magnet is moving backwards). Thus, the magnets automatically reciprocate in lock step (with two magnets always 180xc2x0 out of phase with the third magnet). Accordingly, the pump is capable of pumping fluid on both the forward and back strokes of the piston. On the backstroke, fluid passes over the coil windings, providing fluid cooling, which allows the pump to operate more efficiently and deliver higher output levels.
In yet another embodiment, any one of the above-described pumps can be incorporated into a variety of balloon catheters